spring源码分析系列 (8) FactoryBean工厂类机制

1、FactoryBean设计目的以及使用

FactoryBean对象设计是为了生成简化对象, 在BeanDefinition加载的时候FactoryBean的beanName会带有特殊前缀&.

public interface FactoryBean<T> {
    @Nullable
    T getObject() throws Exception;

    @Nullable
    Class<?> getObjectType();

    default boolean isSingleton() {
        return true;
    }
}

在BeanFactory中的定义:

public interface BeanFactory {
        // FactoryBean前缀, 用于区分FactoryBean产生的bean. 如果myJndiObject为FactoryBean, 可以用&myJndiObject获取工厂类
        /**
         * Used to dereference a {@link FactoryBean} instance and distinguish it from
         * beans <i>created</i> by the FactoryBean. For example, if the bean named
         * {@code myJndiObject} is a FactoryBean, getting {@code &myJndiObject}
         * will return the factory, not the instance returned by the factory.
         */
        String FACTORY_BEAN_PREFIX = "&";
// .........
}

实际应用中如ProxyFactoryBean可以将代理的具体细节隐藏起来, 只需要通过getObject获取代理. 还有CronTriggerFactoryBean配置使用quartz时候简化配置等. 以下为一个示例demo:

DecorationFactoryBean.java

/**
 * bean 装饰工厂
 * @author 
 */
public class DecorationFactoryBean implements FactoryBean<Bean> {
    @Override
    public Bean getObject() throws Exception {
        Bean bean = new Bean() ;
        bean.setName("在FactoryBean统一处理属性") ;
        return bean;
    }

    @Override
    public Class<?> getObjectType() {
        return Bean.class;
    }
}

ioc-FactoryBean.xml

<?xml version="1.0" encoding="utf-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
    <bean >
</beans>

ioc-FactoryBean.xml